1. Field of the Invention
The present invention relates to a scanning optical system, and more particularly, to a scanning optical system utilizing a curved mirror instead of a scanning lens such as an f.theta. lens.
2. Description of the Related Art
A scanning optical system is essential to a laser printer, a laser scanner, a bar code reader or the like. In a scanning optical system, a polygonal mirror, a hologram disk or the like is used as a light deflector. A laser beam emitted from a semiconductor laser is incident upon and deflected by the light deflector. Then the laser beam passes through such a scanning lens system as an f.theta. lens system to scan a predetermined area on a scanning surface (i.e., the main scanning is executed). The scanning surface is, e.g., a sensitive paper or plate. While the main scanning is being executed, the scanning surface is moved in the direction perpendicular to the direction of the main scanning (i.e., the sub-scanning is executed). Thus, the scanning surface is two-dimensionally scanned.
In a conventional arrangement, the laser beam deflected by a light deflector passes through such a scanning lens system as an f.theta. lens system as noted above. However, in the case that a scanning optical system is used as a writing or reading optical system utilizing a multicolor light source, a chromatic aberration occurs. For this reason, in recent years, there has been proposed a scanning optical system utilizing a curved mirror instead of a scanning lens system.